The present invention relates to routing, forming and connecting (collectively, xe2x80x9cconfiguringxe2x80x9d) optical fibers between optical ports such as optical transmitters, receivers/detectors and additional fibers, and more particularly, to configuring optical fibers between optical ports where connection distances are short thus requiring small radius bends in the routing of connection fibers. The present invention further relates to optoelectronic devices involving such optical fiber configurations and apparatus for manufacturing such optoelectronic devices.
Optical fiber communication is an important mode of data transmission around the world due in part to large bandwidth capabilities and freedom from most forms of electromagnetic interference. Additionally, as computer speeds approach one gigahertz (GHz) and beyond, parasitic Resistance, Capacitance and Inductance (RCL) of connecting wires adversely influence data transmission, making direct optical connections more desirable to, between, and within computers and other communication devices. Particularly desirable is the optical connection of all timed devices within a computing device to deliver clock distributions between chips/components in phase or otherwise with a known temporal relationship. In addition, it is not unusual for different timed modules in a device to require different voltages. In conventional wiring arrangements, timing and data transmissions must first be converted to the proper voltage before being relayed from one module to the next. This, along with the RCL problems associated with high speed transfers can cause significant delays of synchronized signals and thus, adversely affect system performance. Optical connections can reduce or eliminate these problems. However, connecting and routing optical fibers between optical ports presents an array of additional problems. These problems include: shear stress at the connection point, difficulty routing due to fiber stiffness, optical distortion caused by adhesives, light leakage from sharp bends, micro fractures, sharp fibers damaging components etc.
There have been numerous attempts to overcome the difficulties in connecting optical ports. One method entails a non-contact alignment of a connecting fiber and the corresponding optical port such that the signal propagates through space. While this method solves several problems, such as shear stress at the connection point, it causes others. For example, components typically must be precisely mounted, directed, and aligned within xe2x80x98eyesightxe2x80x99 of the optical ports, e.g., in a pathway of the transmitted optical beam, within the acceptance angle of an optical fiber end, or in optical alignment with a detector surface of an optoelectric transducer. Other attempts have used optical adhesives to xe2x80x98gluexe2x80x99 optical fibers to optical ports, however, such methods have proven difficult in mass production and often the adhesive has an impact on optical performance.
Another approach involves extruded optic transmission lines between optical transmission ports. This eliminates certain inherent problems with connecting ports with optical fibers. Since the optical pathways are formed in place, they reduce or avoid internal stresses and micro fractures that result from bending an existing optical fiber. Additionally, the extruded optical pathways are easily routed since they are formed in place in a fluid state. However, in order to obtain a good surface adhesion bond between he extruded pathways and the optical port, the temperature of the optical port must generally be elevated to ensure proper bonding. Additionally, if the extruded pathway cools too quickly, clogging can occur at the nozzle of the extruder head. These problems may be addressed by performing these extrusions at an elevated ambient temperature, e.g., between 170xc2x0 and 250xc2x0 Celsius. These elevated temperatures may be problematic in certain contexts involving sensitive components. Finally, such extruded optical pathways generally only address a single connection, from one optical port to a second port, and do not provide a method for forming a series of connections using a continuous optical guide.
This invention addresses problems outlined above providing the desired result of accurately connecting optical ports with an optical fiber in a simple efficient manner and without unduly degrading the fiber or its optical transmission qualities. The invention provides a simple process and associated structure for forming optical connections without intervening adhesives or free space pathways and with minimum heating of the ambient environment. Additionally, the invention allows connecting fibers to be simply lengthened and shortened and annealed in place. Processes and apparatus for fiber alignment and forming multiple connections with a single fiber are also described, as well as the resulting optoelectronic devices.
As used herein, optical ports include active optical transmission elements (such as, electronic chips with light emitters, including but not limited to LEDs, Lasers, or VCSELs (Vertical Cavity Surface Emitting Laser)) active optical receiving elements such as photodiodes and other detectors or photoelectric transducers) and passive transmission/detection elements (such as ends of optical fibers which, in turn, may be associated with active elements). Optical fibers include homogenous single strands and fibers including a core and cladding like modem telecommunication fibers. Preferably, the fiber will contain a core and cladding to improve its optical characteristics. The optical fibers may be made of various materials including quartz, glass or plastic.
According to one aspect of the present intention, a method and corresponding apparatus are provided for connecting an optical fiber between optical ports. The method involves heating an end portion of an optical fiber to soften the end portion, contacting the softened end portion to a first optical port, routing the optical fiber to a second port and connecting the fiber to the second port. In addition, to increase adhesion, the top surface of the optical port or associated structure may also be heated. Preferably, all heating is done using a localized heating process, (e.g. laser or ultrasound heating such that the potential for heat damage to nearby components is reduced. Once softened, the end may be contacted with the port to create an optical coupling. Feedback based on an optical signal transmitted through the fiber may be used for accurate fiber/port alignment as described in more detail below. The fiber is preferably a preformed fiber, accordingly, the step of routing may involve unspooling a length of fiber as well as forming, dimensioning and annealing the fiber by heating as discussed below. The fiber may be optically connected to the second port, for example, by physically terminating the fiber at the second port or by bending and bonding the fiber""s longitudinal edge at the second port. In either case, the fiber may be bonded at the second port by a heating, softening, and contacting process.
As will be appreciated, the inventive optical connection method will work with multiple fiber types including fibers made of glass, plastic or quartz. More particularly, the method can utilize homogenous fibers as well as optical fibers that containing a homogenous core surrounded by a different refractive index light reflecting cladding.
With respect to the optical ports, at least two ports may be connected using an optical fiber for signal transfer therebetween. The connection generally will involve connecting at least one light emitting port with at least one light detecting port. However, connections can also be made between active components (emitters and receivers) and passive or intermediate components such as the end of a telecommunications fiber-optic cable and/or wave guides. As will be appreciated, connection to an intermediate component such as a telecommunication fiber allows the direct connection of an electronic chip to an optical network, especially in contexts where it may be impractical to directly connect the telecommunications fiber to the chip. Additionally, multiple optical ports contained within a computer on optoelectronic chips may be interconnected using the above method. For example, a clock chip within a computer containing multiple optical ports may be connected to numerous time dependent components using multiple fibers. Alternatively, multiple ports may be connected using a single optical fiber creating chain-link connections therebetween as will be further described below. Finally, many fibers may be connected in parallel between optoelectronic chips creating bus connections.
With respect to connecting the fiber to the second port, the fiber may be softened and pressed into contact with the optical port. This may be done using a mechanical pawl that holds the fiber on the port either immediately after or while the localized heating is performed. Again this heating will preferably be done with a focused source such as a laser. Preferably, the pawl is made of a transparent material such that the laser can heat the fiber while the pawl remains in place. As will be appreciated, by using a localized source, not only can the fiber be heated, but the port itself may also be heated to increase the adhesion bond between the port and fiber. Generally, the pawl presses in a direction transverse to the longitudinal axis of the connection fiber to force the fiber into contact with the structure of the second port; this in effect xe2x80x98bendsxe2x80x99 the connection fiber at the connection point. This bend creates a narrowing or xe2x80x98neckxe2x80x99 in the fiber""s cross-section, thus, increasing the angle at which photons within the fiber hit the core/clad interface. Normally, the fiber cladding reflects the photons back into the fiber, however, if the angle at which the photons hit the optical fiber cladding is great enough, light will leak out of the core pass though the cladding and thereby form a connection with the optical port. If the neck angle is great enough, nearly all the photons will exit the fiber, however, if the neck angle is reduced, fewer photons will exit the fiber and the remainder can continue down the fiber. As will be appreciated, this method works with homogenous fibers as well as core and cladding optical fibers.
By utilizing a bending connection with a shallow angle, where some photons continue being refracted within the fiber, multiple optical ports can be connected using a single optical fiber. For example, a light emitting port may be connected to three light detecting ports, where the middle two detecting ports utilize a neck connection as discussed above allowing the light emitting port to be coupled with all light detecting three ports. As will be appreciated, this creates a chain-link connection between the ports and several such fibers connected in parallel may be used to create a bus connection. The above example envisions a simple chain-link or bus connection, however, much more complicated connections are possible within the scope of this invention. According to another aspect of the present invention, an optoelectronic device includes a side-mounted fiber/port interface. Specifically, the device includes an optical fiber and port for transmitting and/or receiving optical signals relative to the optical fiber. The fiber includes a longitudinal axis, along which optical signals propagate, and a side wall defined by the circumference of a cross-section transverse to the longitudinal axis. In accordance with the invention, a connection is formed between the port and a portion of the fiber side wall so that light is transmitted between the port and the fiber through the side wall. The port may be an active port or a passive port.
In one embodiment, the port is a receiver or detector. Light transmitted through the fiber is caused to penetrate the side wall at the location of the port to form an optical connection. The fiber may be of homogenous construction or non-homogenous (e.g., core and cladding) construction. In the latter case, light may also penetrate the cladding to effect the connection. Light may be caused to penetrate the side wall by bending or forming a neck in the fiber so that light is incident on the side wall or core/cladding interface at an angle greater than a critical angle for retaining the light in the fiber which may be related to the fiber""s acceptance angle. The connection may be formed so that some light exits the fiber at the port to form the connection and other light is retained within the fiber and is available for forming serial connections using a single fiber.
According to another aspect of the present invention, a method and corresponding apparatus are provided for routing an existing optical fiber between optical ports without unduly degrading the fiber""s optical transmission qualities. The inventive method includes applying heat to soften the optical fiber as it is routed from one connection point to the next to prevent fracturing the stiff fiber. Preferably, the heating is a localized process, such that the potential for heat damage to nearby components is reduced. A localized heat source as described above may be used to soften the fiber route the fiber. Additionally, to prevent fiber degradation, the method preferably involves retracing and heating the entire length of the optical pathway after connection. As may be appreciated, this post connection softening of the fiber relieves internal stresses of the connected fiber. This softening in turn eliminates shear forces located at the connection between the optical ports and the optical fiber. Last, the post connection softening seals microfractures in the optical connection fiber""s surface preventing undue light leakage and premature breakage.
According to another aspect of the invention, a method is provided for active alignment of the optical fibers with their respective optical ports. In certain cases, optical ports on optoelectronic chips are not easily located by sight or alignment marks or are otherwise susceptible to optical losses due to misalignment. For example, a common practice involves mounting chips upside down on a ball and solder grid and emitting or receiving optical signals through the chip""s substrate. Generally, chips do not contain alignment marks on their substrate making visual location and alignment more difficult. The active alignment method involves disposing a first end of a connecting fiber proximate to the optical port, transmitting an optical signal through the fiber relative to the port, monitoring the signal, and adjusting the position of the connection fiber to maximize the signal transfer. More particularly, one end of the connection fiber may be optically connected to an optical component capable of sending and/or receiving optical signals. The other end is brought into proximity with the optical port. Then, in the case of an emitting port, the connection port is driven to produce a light output. The light output signal is monitored through the attachment fiber. Once the signal is maximized, the above described attachment method or another attachment method is performed. Alternatively, a signal may be transmitted through the fiber to the port, e.g., in the case of a light receiving or passive port to perform the active alignment. In this regard, an output of the port may be monitored to identify a maximum value of the received signal to thereby optimize alignment.
According to a further aspect of the invention, a method is provided to adjust the optical pathway length after connection. As will be appreciated, this is particularly desirable in connecting multiple timed modules to a clock chip, wherein variance in the length of the optical pathways can affect synchronization. The method involves heating a section of the connected optical pathway, causing or allowing a force to act upon the fiber, and adjusting the length of the fiber. More particularly, when increasing length, a section may be heated to a near molten state after which a mechanical force is applied to stretch the fiber. When decreasing the length, the applied force may be the surface tension of the molten fiber, which draws the fiber shorter. As will be appreciated, multiple adjustments may be made on a single fiber if needed.